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Upper GI Anatomy Presented by - Molly HarrimanOutline Gross anatomy, histology, blood supply and innervation of: • Oesophagus • Stomach • Small intestineWhat are the layers of the GI tract?Layers of the GI T ract Mucosa = innermost layer • Epithelium • Lamina propria – contains blood vessels and MALT • Muscularis mucosa – layer of smooth muscle Submucosa • Blood vessels, lymphatics and nerves Muscularis Externa • Inner circular layer • Outer longitudinal layer Serosa / Adventitia = outermost layer • Connective tissueInnervation of the GI Tract system:ed by the autonomic nervous • Parasympathetic – mainly from the vagus nerve (CN X) • Sympathetic – from thoracic and upper lumbar areas of spinal cordEnteric Nervous System 2 plexuses: 1. Myenteric Plexus (Auerbach’s Plexus) • Between the longitudinal and circular layers • Motor neurons • Controls gut motility 2. Submucosal Plexus (Meissner’s Plexus) • Within the submucosa • Motor neurons • Controls secretion from glandsOesophagus • ~ 25cm long • Extends from C6 – T11 (larynx → LOS) • Pierces the diaphragm at T10 = oesophageal hiatus 2 distinct regions: 1. Thoracic oesophagus 2. Abdominal oesophagusWhat epithelium makes up the mucosa of the oesophagus?Histology Mucosa = innermost layer • Epithelium = non keratinized stratified squamous epithelium Submucosa • Contains mucous glands for lubrication Muscularis • Upper 1/3 – striated muscle rd • Middle 1/3 – mixed muscle • Lower 1/3 – smooth muscle Serosa / Adventitia = outermost layer • Thoracic oesophagus = adventitia • Abdominal oesophagus = serosa2 Oesophageal Sphincters Upper oesophageal sphincter • Anatomical sphincter • Voluntary control • Striated muscle Lower oesophageal sphincter • Functional sphincter • Involuntary control • Smooth muscleWhat are the 3 main factors to stop reflux of stomach contents going into the oesophagus? What is the clinical relevance?Blood Supply Thoracic Oesophagus • thoracic aorta) – inferior thyroid artery (branch of • Venous drainage – inferior thyroid vein and azygos vein Abdominal Oesophagus • Arterial supply – left gastric artery and inferior phrenic artery • Venous drainage – left gastric vein (portal circulation) and azygos vein (systemic circulation)Lymphatics rd Upper 1/3 • Deep cervical nodes Middle 1/3rd • Superior and posterior cervical nodes Lower 1/3rd • Left gastric and coeliac nodesWhat are the functions of the stomach?The Stomach regiond primarily in the left hypochondriac region with a small portion in the epigastric Functions • Storage of ingested food • Mechanical breakdown of ingested food • Disruption of chemical bonds in food material through the action of acids and enzymes • Production of intrinsic factor → required for absorption of vitamin B12 Ingested substances combine with the secretions of the glands of the stomach to produce a viscous, highly acidic, soupy mixture of partially digested food → chyme Interior of the stomach has longitudinal folds called rugae → allows for stomach expansion (can be seen in barium swallow)StomachStomachBlood Supply Fundus • Short gastric arteries Lesser Curvature • Right gastric artery (common hepatic artery) • Left gastric artery (coeliac trunk) • Anastomose Greater Curvature • Right gastroepiploic artery (gastroduodenal artery) • Left gastroepiploic artery (splenic artery)Histology Mucosa = innermost layer Epithelium = simple columnar epithelium – extend down into lamina propria where they form columns of secretory cells (gastric glands) Several gastric glands open into large gastric pits Gastric pits contain different types of exocrine cells : • Mucous neck cells – mucous • Chief cells – pepsinogen and gastric lipase • Parietal cells – intrinsic factor and hydrochloric acid • G cells (antrum) – gastrin Submucosa Muscularis • Innermost oblique layer = EXTRA muscle layer • Thickening of smooth muscle = pyloric sphincter (controls entry of chyme from stomach to duodenum) Serosa / Adventitia = outermost layerSmall Intestine Extends from the pyloric sphincter → ileocaecal valve • Duodenum • Jejunum • IleumDuodenum C shaped organ – intimately related to the head of the pancreas Retroperitoneal 4 parts: D1 – Superior part (5cm) D2 – Descending part (7.5cm) D3 – Inferior part (10cm) D4 – Ascending part (2.5cm)Arterial Supply Overview Coeliac trunk (T12) – Foregut • Left gastric artery • Common hepatic artery • Splenic artery Superior Mesenteric Artery (L1) – Midgut Inferior Mesenteric Artery (L2) – HindgutDuodenal Blood Supply Arterial Supply: Gastroduodenal Artery • Supplies →1Ampulla of Vater (7.5cm) Inferior Pancreatoduodenal (branch of superior mesenteric artery) • Supplies Ampulla of→VD4er Venous drainage: Portal veinJejunum • Attached to the posterior abdominal wall via the mesentery • 2.5m • Duodenojejunal flexure • Intraperitoneal • Wider diameter + more folds • Arterial supply – Superior Mesenteric Artery (SMA) • Venous drainage – Superior Mesenteric Vein (SMV) → portal circulationIleum • 3.5m • Continuous with jejunum → ileocaecal valve • Intraperitoneal • Narrow diameter • More mesentery • Peyer’s Patches (lymphoid nodules – MALT) • Arterial supply – Superior Mesenteric Artery (SMA) • Venous drainage – Superior Mesenteric Vein (SMV) → Portal circulationSmall Intestine Histology Mucosa = innermost layer Submucosa Epithelium = Simple columnar epithelium • Contains Brunner’s glands – secrete alkaline mucus to • Villi, Microvilli neutralize acidic chyme (predominantly found in duodenum) 2 main types of cells Muscularis • Absorptive – release enzymes for digestion • Goblet cells – release mucous (alkaline) Serosa = outermost layer Crypts of Lieberkühn - located at the bottom of villous glands • Paneth cells – secrete lysozyme, has an immune function • Enteroendocrine cells – secrete hormones • S cells – secrete secretin • CCK cells – secrete cholecystokinin • K(GIP)s – secrete glucose-dependent insulinotropic peptideSmall Intestine Histology 3 structures facilitate the process of digestion and absorption: 1. Circular folds – Plicae circularis (Valvulae conniventes) 2. contain an arteriole, venule and lacteala which greatly increase surface area, each 3. Microvilli – microscopic projections of plasma membranes of absorptive cells – again increasing surface areaThank you for listening GOOD LUCK!